1. Field Of The Invention
This invention relates generally to the field of communications, and more particularly to control architectures and associated access mechanisms relevant to providing integrated ATM-based services over a shared channel, shared media access network. Specifically, it pertains to a novel method for controlling shared channel access to an upstream channel for multimedia traffic utilizing ATM cell transmission in the shared media of an access network with a tree-and-branch bus topology, with dynamic bandwidth allocation in order to gain efficiency in bandwidth usage and flexibility in subscriber bandwidth allocation. An example of such a shared channel, shared media network is a hybrid fiber-and-coaxial cable network.
2. Description of the Prior Art
Alternate shared channel, shared media approaches grant channel access to a terminal's interface, thereby regulating the terminal's output regardless of the type of traffic, whether it is voice, video or data traffic. While this approach may be suitable for data-only access, it is problematic for access terminals that must transport a mix of voice, video, and data. Common shared channel, shared media networks do not use signaling protocols and do not create connections. This connectionless access, while good for local area networks, has limitations in meeting multimedia service requirements.
Fiber and coaxial cable architectures typical of the CATV industry are under consideration by telephone companies for providing video dialtone broadband services. The fiber/coax architecture may be desirable for providing both narrowband and broadband services. Plain old telephone services (POTS) and narrowband services (n times 64 Kbps) will be provided to each subscriber by allocating a portion of the serving area's bandwidth using a TDMA protocol. Other portions of the telephone companies' access bandwidth will be assigned to broadband video applications such as Cable TV, video-on-demand (VOD), and near-video-on-demand (NVOD). Dedicated channels become bandwidth limited, however, when emerging interactive applications are considered that require throughputs exceeding a few megabits per second for mixes of voice, image, data, or multimedia traffic. Shared channel access for these high bandwidth applications needs to be considered in order to gain efficiency in bandwidth usage and flexibility in subscriber bandwidth allocation.
There are two general approaches for interactive services that are applicable to the hybrid fiber/coax architecture with its shared coaxial medium for subscriber access. The first is a Broadband Metropolitan Area Network (MAN) approach that has evolved from the data communications industry. It has historically been used in traditional CATV-type cable facilities but may find use in the new fiber/coax architecture. Second, an emerging approach tailored to the architecture, uses TDMA for providing digital circuits composed of multiples of 64 Kbps. This is the approach being provided by the telecommunications industry for voice and data services over the fiber/coax network and is referred to here as the Telecom approach.
The Broadband MAN, (BB-MAN), is a metropolitan area network for connectionless data services on fiber/coax networks that uses random access protocols. The broadband MAN is created by frequency translating the upstream signals and broadcasting them downstream. This creates a bus-like appearance to terminals on the coaxial network. The network is intended for data services, and uses LAN technology such as bridges and routers to manage and route traffic.
A newer technology is evolving for use in the fiber/coax architecture. The basic approach is to provide transport of 64 Kbps digital circuits over the coaxial portion of the access network. These 64 Kbps circuits are time division multiplexed and broadcast to all home-mounted Network Interface Units (NIU) that interface subscribers to the network. Typically an NIU has at least one 64 Kbps circuit for providing voice service to a home's analog phones. The NIU's circuits are time division or frequency division multiple accessed onto an upstream channel. This technology provides a narrowband digital access typically with a rate of 64 Kbps and potentially up to about 1.5 Mbps per subscriber within the limits of the serving aread's total upstream bandwidth.
The principal disadvantages of the BB-MAN Approach is that it cannot guarantee the quality of service provided to a subscriber, such as average bandwidth. The access throughput is dependent on network load and its behavior cannot be easily controlled. In cases of heavy use, it could potentially provide a very low grade of service to data users. It has unacceptable performance for delay sensitive multimedia applications and services, and is better suited for e-mail-like data services. BB-MAN's random-access provides a subscriber fluctuating bandwidth as a result of the varying number of subscribers and their applications.
The principal disadvantage of the Telecom approach is that it uses a fixed bandwidth assignment and severely limits available subscriber bandwidth. Bandwidth is provided in multiples of 64 Kbps. The number of 64 Kbps circuits available is limited by the upstream channel bandwidth. This approach is very inefficient, for example, for data applications that tend to be bursty in nature, requiring high bandwidth for short periods of time. Applications that require a high burst rate, for example, 1.5 Mbps, would waste bandwidth if a connection rate of 1.5 Mbps is assigned for the entire call. The number of subscribers and their allowed bandwidth is limited, bounded by the serving area size, channel bandwidth, and the n .times.64 Kbps bandwidth allocation used in this approach. An upper bound on a subscriber's available bandwidth is proportional to the shared channel bandwidth divided by the number of n .times.64 Kbps circuits. For example, consider an upstream aggregate channel rate of 1.5 Mbps and twenty-three subscribers with 64 Kbps data connections. The twenty-fourth subscriber may only have up to 64 Kbps for his application that requires 100 Kbps.
The present invention is directed to the solution of two problems which persist in prior art situations. First, for telephone company provided multimedia services, the service provider will need the ability to manage access traffic and will need to provide quality of service controls and guarantees to the subscriber. Second, a problem for access control protocols with the control in the network is one of allowing access to a newly added terminal, or of reinitializing a terminal after a power failure.
Granting access to a network interface creates a problem for multimedia terminals that need to transmit a mix of voice, video, and data over the terminal's network interface. For shared media networks, such as local area networks, access is granted to the channel by a media access control protocol, MAC. The MAC grants channel access to a terminal's network interface, thereby regulating the terminal's output regardless of the type of traffic, for instance voice or data. For a network that has only one type of traffic, in this example data, this terminal access approach is adequate.
A problem exists, however, if the terminal is transporting mixed traffic types such as video, data, and voice. Each type of traffic from the terminal requires the access control function to provide a special transfer characteristic. Voice traffic requires a low delay access and data traffic requires a bursty access. The problem with prior media access control protocols that grant access to a terminal's network interface is that it restricts the effectiveness of traffic management. A terminal's data traffic could interfere with its voice or video traffic. Such terminal access protocols can not regulate the access based on the type of traffic and support multimedia service requirements.
A centrally controlled network has difficulty learning of newly added terminals (terminals that come on-line) or reinitialized terminals. The network cannot grant access to the upstream channel unless it knows of the terminal's existence and the state of the terminal. Such problems do not exist for random-access networks, for example an Ethernet network, in which a terminal may transmit at any time and announce itself to the network. A problem exists for time-reservation access networks that grant time in the channel, for instance, as in a TDMA network. The network assigns time-slots for established connections with known terminals.
The centrally controlled network must provide some form of terminal initiated transfer without the existence of a connection in the shared channel of the shared media. This connectionless access mechanism is needed for the integrated access described in this disclosure. This integrated access uses a portion of the coaxial cable's RF spectrum that is shared for the transport of ATM user, control, management, and signaling cells. For the special cases of, for example, a newly added or reinitialized terminal, there is no established connection between the terminal and the network (the controller). For these reasons a connectionless access mechanism is needed.
Other approaches to addressing the connectionless access problem require the network to know a finite address list of all terminals on the network. One approach is to periodically poll all terminals by sequencing though a terminal listing to bring new terminals on-line. This is not an efficient approach, because for a large list, much time is spent polling idle terminals.
A principal object of the present invention is to provide control architectures and associated access mechanisms relevant to providing integrated ATM-based services over shared channel, shared media access networks.
A further object of this invention is to address both the upstream traffic management and the connectionless access problems for ATM transmission in the upstream shared channel, by providing a connectionless access mechanism and a method for terminal initiated transfer.
It is a further object of this invention to provide that the service requirements for multimedia traffic, such as quality and rate, can be met.
It is still a further object of this invention to provide a novel method for controlling shared-channel access to an upstream channel for multimedia traffic utilizing ATM cell transmission in the shared media of an access network with a tree-and-branch bus topology, with dynamic bandwidth allocation in order to gain efficiency in bandwidth usage and flexibility in subscriber bandwidth allocation.